Typically, an ideal transducer has an output voltage that is directly proportional to the applied stimulus, such as pressure or temperature. Thus, if the transducer output shows a meter reading that is doubled, one can be assured that the stimulus has also doubled in magnitude. However, there are no really ideal transducers. Most of them include some non-linearities, the greatest non-linearity normally being the second order term of a power series that can be written to represent a transducer output characteristic, such as transducer output voltage. Such second order term is itself proportional to the stimulus, such as pressure, so that if a greater or lesser amount of stimulus is applied, the slope of the output signal from the transducer is increased or decreased in response to the change in that stimulus and the small incremental variations in the applied stimulus will produce different incremental readings on a meter which reads the output signal.
One of the problems in processing signals from such non-linear transducers is the need to adjust by electronic means the output indication so that such indication is corrected for the non-linearities inherent in the transducer itself. Since the non-linearities in the transducer can generally be described in any simple, continuous region by a power series, one can quite exactly correct for the nonlinearities by introducing a counterbalancing term for each of the higher order terms in the power series itself. For example, if there is a 1% positive term that is responsive to the square of the applied stimulus, i.e., pressure, one can correct for that term by introducing a 1% negative term in the amplification of the system that is also responsive to the square of an input voltage applied to the power amplifier of the system.
One means of obtaining the 1% negative term is to reduce the output signal of the transducer slightly under the control of and in proportion to the output signal itself. This can be accomplished in a Wheatstone bridge by applying a smaller voltage to power the bridge so that, as the output signal from the bridge is increased, the input voltage applied to the bridge from a power amplifier is reduced. The linearization or correction of the second order term mentioned above requires only that some portion of the applied or input voltage be responsive to the output signal so that then the total voltage on the transducer, such as a bridge will be proportional to some fixed level and to a component responsive to the applied stimulus.